STRUCTURAL STUDY AND HYDROGEN SORPTION KINETICS OF BALL-MILLED Mg-10 wtNi ALLOY CATALYSED BY Nb

摘要

It is well known that Mg2Ni facilitates hydrogen molecule dissociation in the composite Mg-Mg2Ni and enhances hydrogen diffusion at phase boundaries. To further improve the hydrogen sorption kinetics, Nb has been introduced into Mg-Mg2Ni composite. In the present study, the eutectic structure of cast Mg-10wt%Ni was refined by addition of lwt% Nb into the melt during casting. Chips of cast Mg-10%Ni and Mg-10%Ni-l%Nb were ball milled separately and then with 5 wt% multi-walled carbon nanotubes (MW-CNTs), and 0, 1.5, 3, and 5 mol% Nb. Scanning electron microscope (SEM) analysis was carried out on cast and ball-milled samples to study the microstructure and distribution of Nb and Mg2Ni. The absorption and desorption kinetics of samples were measured at 350, 250, and 200°C by Sievert's method apparatus. The results showed that l%Nb addition during casting accelerates the hydrogen diffusion compared to cast Mg-10 wt%Ni without Nb. Moreover, addition of 5% MWCNTs to ball-milled powders improved the activation characteristics of the samples significantly. The absorption/desorption kinetics, as well as the hydrogen capacity of the sample containing 1.5% Nb were improved considerably even at temperatures as low as 100°C. Thermogravimetric analysis/ differential scanning calorimetry (TGA/DSC) results showed that the releasing temperature decreased by approximately 100°C compared to the ball-milled Mg-10 wt%Ni sample with no Nb.